The X-ray Fundamental Plane of Clusters of Galaxies Yutaka Fujita National Astronomical Observatory, Japan We analyze the relations among central gas density, core radius, and temperature of X-ray clusters by plotting the observational data in the three-dimensional (log  gas;0 , log r c , and log T gas ) space and nd that the data lie on a 'fundamental plane'. ... The two parameters describing the plane are formation redshift and temperature of clusters. ...